The result is a starry sky visible even from the heart of the city. Flagstaff’s Buffalo Park, just a couple miles from downtown, measures about a 4 on the Bortle scale, which quantifies the level of light pollution. (The scale goes from 1, the darkest skies possible, to 9, similar to the light-polluted night sky of, say, New York City. To see the Milky Way, the sky must be below a 5.)

A 400-mile blanket of fog has socked in California’s Central Valley for weeks. Scientists and meteorologists say the conditions for such persistent cloud cover are ripe: an early wet season, cold temperatures and a stable, unmoving high pressure system.

But take a stroll through X, Instagram or TikTok, and you’ll see not everyone is so sanguine.

People are reporting that the fog has a strange consistency and that it’s nefariously littered with black and white particles that don’t seem normal. They’re calling it “mysterious” and underscoring the name “radiation” fog, which is the scientific descriptor for such natural fog events — not an indication that they carry radioactive material.

An X user with the handle Wall Street Apes posted a video of a man who said he is from Northern California drawing his finger along fog condensate on the grill of his truck. His finger comes up covered in white.

“What is this s— right here?” the man says as the camera zooms in on his finger. “There’s something in the fog that I can’t explain … Check y’all … y’all crazy … What’s going on? They got asbestos in there.”

Another user, @wesleybrennan87, posted a photo of two airplane contrails crisscrossing the sky through a break in the fog.

“For anyone following the dense Tule (Radiation) fog in the California Valley, it lifted for a moment today, just to see they’ve been pretty active over our heads …” the user posted.

Scientists confirm there is stuff in the fog. But what it is and where it comes from, they say, is disappointingly mundane.

The Central Valley is known to have some of the worst air pollution in the country.

And “fog is highly susceptible to pollutants,” said Peter Weiss-Penzias, a fog researcher at UC Santa Cruz.

Fog “droplets have a lot of surface area and are suspended in the air for quite a long time — days or weeks even — so during that time the water droplets can absorb a disproportionate quantity of gasses and particles, which are otherwise known as pollutants,” he said.

He said while he hasn’t done any analyses of the Central Valley fog during this latest event, it’s not hard to imagine what could be lurking in the droplets.

“It could be a whole alphabet soup of different things. With all the agriculture in this area, industry, automobiles, wood smoke, there’s a whole bunch” of contenders, Weiss-Penzias said.

Reports of the fog becoming a gelatinous goo when left to sit are also not entirely surprising, he said, considering all the airborne biological material — fungal spores, nutrients and algae — floating around that can also adhere to the Velcro-like drops of water.

He said the good news is that while the primary route of exposure for people of this material is inhalation, the fog droplets are relatively big. That means when they are breathed in, they won’t go too deep into the lungs — not like the particulate matter we inhale during sunny, dry days. That stuff can get way down into lung tissue.

The bigger concern is ingestion, as the fog covers plants or open water cisterns, he said.

So make sure you’re washing your vegetables, and anything you leave outside that you might nosh on later.

Dennis Baldocchi, a UC Berkeley fog researcher, agreed with Weiss-Penzias’ assessment, and said the storm system predicted to move in this weekend will likely push the fog out and free the valley of its chilly, dirty shawl.

But, if a high pressure system returns in the coming weeks, he wouldn’t be surprised to see the region encased in fog once again.